1. Field of the Invention
The present invention relates generally to a wireless power transmitter and method of controlling the same, and more particularly, to a wireless power transmitter and method for transmitting wireless charging power to a wireless power receiver.
2. Description of the Related Art
Mobile terminals, such as cell phones, Personal Digital Assistants (PDAs), etc., are powered by rechargeable batteries, which are recharged with electric energy provided using separate charging devices. For example, for a charging device and a battery having contacting terminals on their outer surfaces, the battery is electrically connected to the charging device by having their contacting terminals contact each other. However, when using such a contact charging method, the contacting terminals are susceptible to contamination by dirt or corrosion when exposed to moisture because they are exposed on the outer surfaces if the charging device and the battery. Obviously, any contamination or corrosion will negatively affect charging.
To address this problem, wireless charging or contactless charging technologies have been developed.
Wireless charging technology uses wireless power transmission and reception. For example, a battery of a cell phone can be wirelessly charged merely by placing the cell phone on a charging pad, without connecting or plugging in a separate charging connector. Wireless charging technology is commonly applied to electric toothbrushes or shavers.
There are a number of different wireless charging technologies, i.e., an electromagnetic induction method using coils, a resonance method using resonance, and a Radio Frequency (RF)/micro wave radiation method that converts electric energy into microwaves for transmission.
The electromagnetic induction method transfers power between primary and secondary coils. Specifically, moving a magnet through a coil produces an induced current from which a magnetic field is produced at a transmission end, and the change in the magnetic field at a receiving end induces a current to generate energy therein. This phenomenon is commonly referred to as magnetic induction, and a power transmission method based on magnetic induction provides superior energy transmission efficiency.
The resonance method uses a resonance-based power transmission principle based on the Coupled Mode Theory, i.e., a physical concept that a tuning fork being placed next to a wine glass causes the wine glass to ring with the same frequency. However, in resonance-based power transmission, resonated electromagnetic waves carry electric energy, instead of resonating sound. Resonant electric energy of the electromagnetic waves is directly transferred to a device having the same resonant frequency, and the non-used part of the energy is re-absorbed into the magnetic field rather than being dispersed in the air. As a result, resonant electric energy is not deemed harmful to surrounding machines or bodies.
Although various studies on wireless charging methods have been done, standards for prioritizing wireless charging, searching for wireless power transmitters/receivers, selecting a communication frequency between a wireless power transmitter and receiver, adjusting wireless power, selecting a matching circuit, distributing communication time for each wireless power receiver in a single charging cycle, etc., have not been provided. In this regard, a need exists for standardization relating to a method of detecting wireless power receivers by a wireless power transmitter.